The proposed research focuses on mutagenic analysis of the GABA (gamma- aminobutyric acid) transporter. This work should be of general interest: 1) as a model system to clarify the mechanism by which presynaptic neurotransmitter reuptake proteins regulate synaptic transmission, and 2) as a model system in which to clarify the role of presynaptic neurotransmitter reuptake protein in central nervous system diseases. Neurotransmitter reuptake into the presynaptic nerve terminal is the dominant mechanism for terminating synaptic transmission mediated by a wide array of the small molecule neurotransmitters (e.g., epinephrine, norepinephrine, serotonin, taurine, aspartate, glutamate, glycine, and GABA). Such neurotransmitters are removed from the synaptic cleft by specific, high-affinity, (Na+ and C1-)-dependent transport proteins. Although transport proteins from this class are directly relevant to several commonly occurring medical conditions - including drug dependence (norepinephrine transporter/cocaine receptor), clinical depression (serotonin transporter/antidepressant receptor), and epilepsy (GABA transporter/anticonvulsant receptor) - it has not been possible until recently to study any of these transporters in molecular detail. To date, information concerning the relationship between the function of these transporters and their molecular structure is completely lacking. The proposed research will make a significant contribution in this area by using mutagenesis to probe structural aspects of the GABA transporter that are functionally important. The applicant has already developed the expression systems required to use mutagenesis as a means of probing structure/function relationships in the GABA transporter, and is pursuing a research plan to: 1) Engineer specific alterations into the GABA transporter using oligonucleotide-directed mutagenesis; 2) Evaluate the functional consequence of mutation by expression in mouse fibroblasts. In broadest terms, the applicant's proposal is significant in that the methodologies developed specifically to the study of structure/function relationships in the GABA transporter should be widely applicable to the genetic characterization of other neurotransmitter reuptake proteins. More specifically, structural information gained from mutagenesis of the GABA transporter may speed the development of novel anticonvulsants acting to inhibit the GABA transporter in brain.